Switching matrix and method for specifying a switching matrix

ABSTRACT

A method of specifying a switching matrix over a Bene{hacek over (s)} network involves specifying a first number of ingress ports and a second number of egress ports for the matrix. Switching elements and connections between the switching elements are configured to the number of ports, and the matrix is subdivided into a plurality of sections. The switching elements and ports are moved and/or turned to obtain certain configurations, but connections are retained.

TECHNICAL FIELD

The present invention relates to a method for specifying a switchingmatrix. Devices and software programs embodying the invention are alsodescribed.

BACKGROUND

Current telecommunications networks supply a variety oftelecommunications services to customers, for example via aMulti-Service Access Node (MSAN). The provided services can comprise forexample Plain Old Telephone Services (POTS), Digital Subscriber Lines(DSL) or Integrated Services Digital Network (ISDN) lines. The servicesare supplied via customer subscriber lines, for example copper cables,connected to a customer Main Distribution Frame (MDF). The MainDistribution Frames play a vital role in an operator network as a resultof the investments required to create a geographically distributedaccess network supporting the delivery of the services to thesubscribers. The access network is a significant asset and any change tothe architecture drives significant incremental cost. Correspondingly,the costs of implementing new technical solutions in the access networkare high and appropriate solutions are often not available on themarket.

Traditionally, the number of required reconfigurations per time periodwas relatively low in the access network. Increased competition,regulatory changes, and the introduction of new services are now drivingmore reconfigurations. Greater numbers of competitive operators takingadvantage of Local Loop Unbundling and the evolution of new broadbandxDSL services are increasing the rate at which subscribers either changetheir service or change from one operator to another. Greater pressureis also placed on access network operators as the location of networkdevices such as a DSLAM (Digital Subscriber Line Access Multiplexer) ismoving from the central office to the MDF as primary connection point,i.e. the location where links from the central office are connected tothe links to the individual subscribers. This is due to the requirementto reduce connection lengths so that high bit rate services such asADSL2+ or VDSL2 can be supported for which the rate drops significantlywith increasing connection length between subscriber equipment andDSLAM.

The customer MDF is usually located in a service box near to thecustomers premises. An MSAN is connected to a provider MDF which is alsolocated in the service box. To supply a particular telecommunicationsservice to a customer the service provider must make connections betweenthe customer MDF and the provider MDF. Such connections are typicallymade manually by a service engineer who must visit the service box andmake the connections. New connections are required to be made each timea new service is provided to a customer or an existing service ischanged. The problem is to manage physical connections for the servicesavailable to the customers, in particular for a big number of customers,e.g. if new customers or new services are added, or when old customerschange the service package or terminate one or more services. All thesechanges traditionally require a visit of the field engineer at theservice box. With regard to the huge number of such service boxesdeployed servicing of them and maintaining high responsiveness tocustomers' requests is both expensive and time consuming.

The cost of making the connections has two main components. The first isthe fixed cost of providing the equipment to make the connection. Thesecond is the overhead cost associated with the requirement for theservice engineer to visit the service box and make the connection.Service providers aim to minimize both of these costs. The overhead costcan be reduced by waiting until there are several connections to be madeat the service box at the same time. This has the drawback that acustomer may have to wait for the service to be connected. Typicallyabout 5-10% of customer connections are changed per year, which meansthat 90-95% of connections remain unchanged. Therefore, waiting toproviding new services to customers is often not a feasible option.Alternatively service providers can minimize the overhead cost byincluding a switching matrix between the customer MDF and the providerMDF which allows automated connections to be made from a remotelocation.

Switching matrixes used for such automated or remote provisioningcomprise cross bar, Bene{hacek over (s)} or Clos networks. Bene{hacekover (s)} networks consist of a plurality of stages of interconnectedswitching elements which allow connecting ingress and egress ports ofthe switching matrix over paths which can be changed according to thestates of the individual switching elements. Cross bar, Bene{hacek over(s)} and Clos networks can provide non-blocking functionality. Whereascross bar and Bene{hacek over (s)} network are non-blocking, a Closnetwork can be either blocking, non-blocking or non-blocking afterreconfiguration. One problem associated with the cross bar is theinitial cost of deployment which increases the fixed costs because thenumber of cross bars increases with a square relationship between thenumber of cross bars and the number of cross paints.

A problem in existing networks is that the number of connections to theMDF is specified by the existing cables and the switching matrix needsan according number of ingress and egress ports. For example, the cablefrom the provider MDF to the central office of the operator may have 100lines and the customer MDF may be designed for the connection to 100lines to the subscribers. In contrast, a Bene{hacek over (s)} networkcomprising 2×2 switching elements is suitable to connect 2^(n) ingressports with 2^(n) egress ports where n is an integer. For numbers ofingress and egress ports which deviate from integer powers of 2, thenumber of switching elements can be reduced without loss offunctionality, e.g. the non-blocking properties, in order to save spaceand costs for the switching matrix. Accordingly, the correspondingnetwork can be called a reduced Bene{hacek over (s)} network. However,the reduced number of ports and switching elements causes an asymmetryin the switching matrix. This leads to increased production costs, inparticular if the size of the switching matrix requires a subdivisiononto a plurality of different circuit boards.

SUMMARY

In view of the above disadvantages it is an object to provide aswitching matrix which can effectively be produced and a method forspecifying such a switching matrix.

In the proposed method, a switching matrix is specified for connectingselected ingress ports to selected egress ports over a Bene{hacek over(s)} network. The Bene{hacek over (s)} network comprises a plurality ofinterconnected switching elements. Each switching element has at leastone input and at least one output and is adapted to connect a selectedinput to a selected output of the switching element. The switchingelements are arranged in stages. The at least one input of any of theswitching elements has a connection to the at least one output of one ofthe switching elements in a preceding stage or to one of the ingressports. The at least one output of any of the switching elements has aconnection to the at least one input of one of the switching elements ina subsequent stage or to one of the egress ports.

A first number of ingress ports and a second number of egress ports ofthe switching matrix are specified, at least one of said numbersdeviating from an integer power of 2 or from the other number. Thenumber of the switching elements and the number of the connectionsbetween the switching elements are adapted to the specified numbers ofports. The switching matrix is subdivided into a plurality sections.

The switching elements and the ports are moved such that at least two ofthe sections comprise an equal number and arrangement of the switchingelements and an equal number and arrangement of the ports, wherein theconnections are retained. In at least one of the at least two sections,switching elements having a connection to a switching element in anotherof the plurality of sections are turned such that the positions of theinputs are interchanged and/or the positions of the outputs areinterchanged. The connections of the turned switching elements to otherswitching elements are retained if the other switching elements aredisposed in a stage in which at least one switching element is turned.The connections of the turned switching elements to other switchingelements are swapped if the other switching elements are disposed in astage in which no switching element is turned. The steps of turning andswapping are performed such that the arrangements of the connectionswithin the at least two sections correspond to each other.

Furthermore, the invention is embodied in a switching matrix asdescribed below, and in a circuit board as described below. Advantageousembodiments are also described below.

The invention can also be embodied in a program used in the execution ofthe method. The program is for example stored on a data carrier orloaded into a processing system of a computer.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the following detaileddescription of preferred embodiments as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of connecting subscriber lines using a switchingmatrix

FIG. 2 shows an example for ingress and egress ports of a switchingmatrix

FIG. 3 shows switching states of a switching element

FIG. 4 shows a high level representation of a switching matrix

FIG. 5 shows a switching matrix with a first option for a rearrangementof the switching elements

FIG. 6 shows a switching matrix with a further option for arearrangement of the switching elements

FIG. 7 shows a flow chart of the proposed method

DETAILED DESCRIPTION

An example of providing different services over a switching matrix to asubscriber line is shown in FIG. 1. A main cable to the central officewith a plurality of central lines 1 is connected over a provider maindistribution frame PM to the switching matrix 100. Furthermore, theswitching matrix 100 is connected over a customer main distributionframe CM to a plurality of subscriber lines 2.

For simplicity only external interfaces of the switching matrix 100 areindicated which allow connecting the switching matrix to other devices.For example, interface A can be used to connect individual subscriberlines with the switching matrix. Interface B can connect the switchingmatrix to other nodes in the operators' network, for example to aswitching node. Interfaces C and D allow to connect different ports ofthe switching matrix with each other. One or more splitters in theinterconnections can provide access to other services, for example tobroadband access using a DSLAM. It is also possible to interconnect aplurality of switching matrixes over the interfaces.

Correspondingly, switching matrix 100 can be used for subscriber lineexchange, i.e. to connect subscriber lines in a flexible way to nodes inthe operator network, to provide access to services and to rearrangethese connections and accesses in a flexible way. Preferably, theswitching matrix 100 is also provided with an interface for remotelyperforming the subscriber line exchange by remotely changing the pathsthrough the switching matrix.

The switching matrix 100 comprises external ports which are denoted asingress and egress ports throughout this specification. However, itshould be noted that it is not relevant for the present inventionwhether a particular port is an ingress or egress port. The portscorrespond to the external interfaces A-D of the switching matrix 100.The switching matrix comprises furthermore a plurality of interconnectedswitching elements, which can comprise for example relays, motor-basedsliders, or micromechanical switches. Relays are especially suited fortough environments, e.g. outdoor applications, as they toleratetemperature changes, vibration and humidity. Relays have also shortswitching times, high voltage endurance as well as low attenuation andcross-talk. The interconnected switching elements provide the pathsthrough the switching matrix which connect selected ingress to selectedegress ports. For a remote service adaptation, the states or settings ofthe switching elements and thus the paths can preferably remotely bechanged.

The example of FIG. 1 shows how an additional service can be provided toa subscriber line. A selected subscriber line 2 arriving at the customerMDF CM is originally connected via path 110 to a selected central line1. When the subscriber of the line 2 wants to have also DSL access as anexample for the additional service, original path 110 is changed to anew path. The broken line represents a removed segment of the originalpath. Instead of the removed segment, new segments of the path areswitched to interfaces C and D of the switching matrix 100. Interfaces Cand D are connected to the inlet 3 and outlet 5 of a splitter. Thesplitter is connected with a further path segment 4 to a DSLAM forproviding a DSL service via optical fibers. Thus the services providedto a subscriber can be easily adapted by controlling the switchingelements and thus the paths through the switching matrix.

A plurality of services can be provided to any selected subscriber line2 in this way. It is both possible to connect one or more additionalservices to a subscriber line via splitters, e.g. on interfaces C and D,and to connect the subscriber lines to central lines 1 which terminatein specific MDFs for the respective service in the central office, e.g.providing POTS service, ISDN, integrated narrow- and broadband likeISDN/ADSL or leased lines. As indicated, the arrangement can connectdifferent access technologies underlying the services. For example,lines 1 and 2 can be copper pairs while the DSLAM connects to opticalfibers.

FIG. 2 shows an example for ingress and egress ports of a switchingmatrix SM. In the example of FIG. 2, the ingress ports are denoted withan A and the egress ports are denoted with a B. 100 ports in four groupsof 25 ports A1-4 and B1-4 on each side allow for example the connectionof subscriber lines to the switching matrix SM and the connection of 100lines of one or more central cables, e.g. to a central office orswitching node of an operator. 50 further lines on each side allow forexample the connection to splitters or distribution matrixes so that apart of the subscriber lines can be provided with additional services.Finally, there are also 2 ports for testing purposes TA and TB on eachof the sides. As a result, the depicted switching matrix has a total of152 ingress ports and 152 egress ports.

FIG. 3 shows two switching states of a 2×2 switching element as it canbe used in a switching matrix for switching different connections andpaths. The switching element is indicated by a square and has two inputson one side and two outputs on the other side. As it is not relevant ifa contact of the element is an input or an output, they are notdistinguished in the figure. In a first state on the left side of FIG.3, the switching element connects the upper input with the upper outputand the lower input with the lower output, i.e. both inputs areconnected in parallel to the corresponding output. In a second stateshown on the right side of FIG. 3, the switching element connects theupper input with the lower output and the lower input with the upperoutput, i.e. the inputs are cross-connected to the respective otheroutput. The upper part of FIG. 3 shows simplified representations of theswitching states while the lower part indicates how these states can berealized with change-over contacts, for example relays.

The interconnection of any ingress port to any egress port of aswitching matrix can be realized with a Bene{hacek over (s)} networkconsisting of interconnected 2×2 switching elements. An advantage of aBene{hacek over (s)} network are the non-blocking properties, i.e. apath between any selected ingress and egress port of the switchingmatrix can be switched as long as the respective ports are still freeregardless of other paths already switched through the network. Incontrast, paths in a blocking network may also block connections toports to which they are not connected.

The number of ingress and egress ports in a regular Bene{hacek over (s)}network is an integer power of 2, i.e. 2^(n) with n being an integer. Ifa regular Bene{hacek over (s)} network shall be used to connect otherarbitrary numbers of ports, the number of ports in the regularBene{hacek over (s)} network must be at least equal to the maximum ofthe arbitrary number of ingress ports and the arbitrary number of egressports. For connecting a first number of ingress ports to a first numberof egress ports, a regular Bene{hacek over (s)} network is thus requiredin which 2^(n) is at least equal to the first number. In the exampledepicted in FIG. 2, the regular Bene{hacek over (s)} network would thushave 256 ingress and 256 egress ports. However, because only some ofthese ports are used in the switching matrix of FIG. 2, the number ofports and switching elements can be reduced to obtain a reducedBene{hacek over (s)} network without changing the number of possiblepaths from ingress ports to egress ports through the network as it isshown in following table 1.

TABLE 1 Example of a reduced switching matrix m_A  152 number of ingressports m_B  152 number of egress ports n  256 number of ingress/egressports if mapped to regular Bene{hacek over (s)} network L  15 number ofstages of Bene{hacek over (s)} network K_max 3840 number of relays oftotally equipped regular Bene{hacek over (s)} network K_saved 1344number of saved relays K_required 2496 number of required relays form_A/m_B ports s_A, i number of saved relays in ith stage counted fromingress R_A, i number of saved relays in completely removed elements inith stage counted from ingress s_B, i number of saved relays in ithstage counted from egress R_B, i number of saved relays in completelyremoved elements in ith stage counted from egress i s_A r_A s_B r_BSaved ports 104 104 1 104 104 104 104 2 104 104 104 104 3 104 104 104104 4 104 96 104 96 5 96 96 96 96 6 96 64 96 64 7 64 0 64 0 8 0 0 0 0

For reducing the number of ports and switching elements, the switchingmatrix is mapped onto the smallest regular Bene{hacek over (s)} networkwhich can accommodate the reduced Bene{hacek over (s)} network of theswitching matrix. The ports of the switching matrix are arranged in sucha way on the regular Bene{hacek over (s)} network that the number ofswitching elements is maximized in which both inputs are connected toingress ports or both outputs are connected to egress ports. As aresult, other switching elements in the ingress and egress stages of theswitching matrix are not connected to any ingress or egress port,respectively. Switching elements in the input and output stage which arenot connected to an ingress or egress port, respectively, are removed.Then in every subsequent stage until the center stage of the Bene{hacekover (s)} network is reached, the number of switching elements ismaximized in which both inputs are connected to switching elements inthe preceding stage toward the ingress side. From the egress side inevery subsequent stage until the center stage of the Bene{hacek over(s)} network is reached, the number of switching elements is maximizedin which both outputs are connected to switching elements in thepreceding stage toward the egress side. Switching elements withoutconnections to the respective preceding stage are removed. Table 1 showsthe number of elements which can be saved compared to a regularBene{hacek over (s)} network both in each stage and in total.

In case that a switching element has one input connection and two outputconnections or two input connections and one output connection, it canbe replaced by a 2×1 switching element in which the single input canalternatively be connected to both outputs or the single outputalternatively to the inputs. This can also decrease the production costsby using simpler switching elements. In particular, a 2×2 switchingelement can comprise two relays as shown in FIG. 3 while a 2×1 switchingelement can be a single relay. A switching matrix SM with 2496 relays in15 stages can thus be obtained in the case of Table 1 and FIG. 2.

This procedure can also be illustrated for a regular Bene{hacek over(s)} network with 56 switching elements in seven stages S1-S7, eachstage in the equivalent regular Bene{hacek over (s)} network consistingof 8 switching elements. Such a switching matrix is shown on the leftside of FIGS. 5 and 6. It is assumed that twelve connections arerequired in the outermost stages S1, S7 for connecting towards the portsof the switching matrix. In contrast, the corresponding regularBene{hacek over (s)} network has 16 ingress and 16 egress ports. As onlytwelve ingress and egress ports are required, two switching elements SEcan be removed in the outermost stages S1, S7 as indicated by thediagonal bars. In the example, these are switching elements 7 and 8 inthe uppermost stage S1 and switching elements 1 and 2 in the lowermoststage S7. Connections CO between the stages are indicated by lines.However, the removed switching elements do not require a connection,i.e. the corresponding connections can also be removed. This isindicated by connections in broken lines.

In both the second stages S2, S6 from the ingress and egress, i.e.counted from the outside of the matrix, there are two switchingelements, i.e. switching element 4 and 8 in the second stage 52 from thetop; switching element 1 and 5 in the second stage S6 from the bottom,which have no connection to the next outer stage S1, S7 and canaccordingly also be removed. Again, the corresponding connectionsbetween stage S2 and the next inner stage S3 as well as between stagesS6 and S5 can be removed as well. In the third stages 53, S5, eachswitching element has a connection to the second stage. However, four ofthe switching elements have only one connection. While those switchingelements cannot be removed without loss of potential paths through thematrix, i.e. inferior non-blocking properties, they can be replaced by2×1 switching elements without this disadvantage. This is indicated by a1:2 below the corresponding switching elements. Finally, all switchingelements in the center stage S4 have two connections on each side. Thusneither the switching elements nor their connections can be removed.

FIG. 4 shows a high level representation of a switching matrix whichdoes not show individual switching elements and connections but only thestages of the Bene{hacek over (s)} network represented by horizontalbars in which the switching elements are disposed. Comprising 15 stages,the switching matrix is suitable for up to 256 ingress and egress portseach if the stages are equipped with 2×2 switching elements. However,due to size limitations and the required number of switching elements itis often difficult or impossible to arrange the switching matrix on asingle circuit board. For example, a supporting rack for the switchingmatrix and/or the service box housing the switching matrix may limit thesize of the circuit boards. This may particularly be the case if theservice box houses further equipment like an MSAN apart from the MDFsaccommodating connections to the cables. In such cases, it is requiredto subdivide the switching matrix into different sections. The sectionscan be interconnected via the backplane, i.e. a support holding thesections of the switching matrix. One example of such a subdivision isshown in FIG. 4.

It should be noted that the above described process of removingswitching elements reduces the symmetry of the switching matrix. Aregular Bene{hacek over (s)} network is point symmetric to the centerpoint of the network, mirror symmetric to the central stage, and mirrorsymmetric to the plane perpendicular to the central stage through thecenter point, i.e. to the plane dividing the network perpendicular tothe stages into two halves. Generally, further symmetries exist. Whenremoving elements at least some symmetries are lost and, in contrast toa regular Bene{hacek over (s)} network with 2^(n) ingress and with 2^(n)egress ports, 2^(n) sections of the switching matrix can generally notbe selected in such a way that they are identical in layout (withintegers m<n). A reduced symmetry increases the costs of production asdifferent boards need to be designed for the sections. If the switchingmatrix is subdivided into four sections as shown in FIG. 4, fourdifferent circuit boards might be required.

Two attempts to resolve this problem are described using the example ofthe switching matrix in FIG. 5 which consists of switching elements SEand connections CO. As indicated by the vertical line the switchingmatrix is subdivided into two sections. Any connections between thesesections are retained but need to be made across the borders of thesections, e.g. via a backplane BP on which the circuit boards for thesections are mounted or in another suitable way. Accordingly, at leastone segment of such a connection is located outside a section, e.g.circuit boards, if the sections are disposed with a distance to eachother.

As indicated by the arrow, the switching elements and connections can berearranged to arrive at a switching matrix with the same functionality.The left part of FIG. 5 shows, as described before, a switching matrixwith a minimum number of switching elements for the selected number ofconnections from the ports (here 12 in each outermost stage).

The upper part of FIG. 5 shows one option for achieving the sameswitching functionality with a different arrangement of the switchingelements: it is possible to make identical arrangements in both sectionsin the first stage S1 by exchanging the positions of switching elements4 and 7. This allows also having identical connections in both sectionsbetween stages S1 and S2. However, when comparing the changes requiredin stage S2 to retain the functionality it becomes obvious that thisoption is disadvantageous. While switching elements 4 and 8 can betotally omitted on the left side of FIG. 5, four 2×1 switching elementsare required on the right side. In stage S3, 2×2 switching elements arenow required instead of 2×1 switching elements. As a result, theoptional rearrangement in stage S1 results both in a higher number ofswitching elements and more connections and optionally also in elementswith more complicated functionality if the switching matrix shall havethe same functionality as on the left side of the figure.

In the lower part of FIG. 5, a second option is shown in which only thearrangement of the switching elements is changed while the numbers andtypes of switching elements in total and in each of the stages S5-S7 arethe same. The number of connections is unchanged compared to the leftside of the figure. Accordingly, the above disadvantages are avoided.Also the arrangement of the switching elements in the two outermoststages S7 and S6 is identical in both sections. However, this leads totwo other disadvantages: In stage S5 different types of switchingelements are required in both sections and the arrangement of theconnections in the sections is different. Thus different circuit boardswould be required for both sections.

With this background and referring to FIG. 7, a method is proposed tospecify a switching matrix for connecting ingress ports to selectedegress ports over a Bene{hacek over (s)} network. The Bene{hacek over(s)} network comprises a plurality of interconnected switching elements.Each switching element has at least one input and at least one output.Preferably, the switching matrix comprises 2×2 switching elements with 2inputs and 2 outputs, optionally also 2×1 switching elements with 2inputs and 1 output or with 1 input and 2 outputs. Such switchingelements are easy to produce and allow any connection between a selectedingress and a selected egress port. The switching elements are adaptedto connect a selected input to a selected output of the switchingelement. Depending on the type of the switching element, it is possiblethat there is only one or a plurality of simultaneous connectionsthrough it. For example, a 2×2 switching element can connect the inputseither in parallel or crossed to the outputs while a 2×1 switchingelement can alternately connect the inputs to the output.

The switching elements are arranged in stages, i.e. for every switchingelement in a selected stage there exists a specific first number ofswitching elements over which it can be connected to ingress ports and aspecific second number of switching elements over which it can beconnected to egress ports. The at least one input of any of theswitching elements has a connection to an output of one of the switchingelements in a preceding stage towards the ingress ports or to one of theingress ports. The at least one output of any of the switching elementshas a connection to an input of one of the switching elements in asubsequent stage towards the egress ports or to one of the egress ports.As was mentioned already before with respect to the terms ingress andegress as well as input and output, also the terms preceding andsubsequent are merely used to specify the corresponding connections anddo not imply a direction of the propagation of signals. Generally, aswitching element in any selected stage is thus connected to switchingelements in stages or ports adjacent to the selected stage.

In the proposed method, a number of ingress ports and a number of egressports of the switching matrix are specified in step 802. At least oneport number deviates from an integer power of 2 or—unless both numbersare equal—from the other number. Preferably, both numbers are identical,i.e. the method is especially suited in case of equal port numbersdeviating from an integer power of 2. Correspondingly, a regularBene{hacek over (s)} network with 2^(n) ingress ports and 2^(n) egressports, where n is a natural number, would comprise at least one unusedport when accommodating the switching matrix, i.e. the network of theswitching matrix. This means that the number of connections and/or thenumber of switching elements can be reduced without loss of switchingfunctionality, i.e. switching elements and/or connections connectingonly to unused ports can be removed. Alternatively or in addition,switching elements can be replaced by switching elements with a smallernumber of inputs or outputs. Accordingly, the number of switchingelements and the connections between the switching elements are adaptedto the port number in step 804. This means that the Bene{hacek over (s)}network of the switching matrix is a reduced Bene{hacek over (s)}network.

The switching matrix is subdivided in step 806 into a pluralitysections. The switching elements and the ports are moved in step 808such that at least two of the sections comprise an equal number andarrangement of the ports and an equal number and arrangement of theswitching elements. The connections between the switching elements areretained when moving switching elements and ports. Preferably, allsections comprise an equal number and arrangement of switching elementsand ports after the steps of subdividing and moving are performed. If aswitching matrix shall be fully subdivided into identical sections thenumber of ports and switching elements must be divisible accordingly,i.e. by the number of sections. The switching elements in the centralstage of such a switching matrix are disposed on all sections, as shownin the examples of FIGS. 4 and 6. In this case, the central stage issplit into a number of parts corresponding to the number of sections.

Moving the switching elements in this way while retaining theconnections has the consequence that the connections within the sectionsare differently arranged. This can be resolved by step 810 of turningswitching elements in at least one of the sections with equal number andarrangement of the switching elements such that the positions of theinputs are interchanged and/or the positions of the outputs areinterchanged. In case of a 2×2 switching element this means that thepositions of both inputs are interchanged and the positions of theoutputs are interchanged. In case of a 2×1 switching element this meansthat the positions of both inputs are interchanged while the singleoutput remains unchanged and for a 1×2 switching element both outputsare interchanged while the input is unchanged.

Turning of a switching element results only in an equal arrangement ofthe connections in different sections if the turned element is connectedto a switching element in another section, i.e. if a connection with theturned element crosses the border of a section. Therefore, the step 810of turning switching elements can be limited to these elements whileother switching elements need not to be turned.

Optionally, the step of turning switching elements can be restricted tostages with connections crossing a border perpendicular to the stages,i.e. a vertical border in FIG. 6. This option simplifies the step ofturning significantly. Furthermore, at most half of the switchingelements in a stage need to be turned. If there are two corresponding,i.e. equally arranged, switching elements in different sections, onlyone of them needs to be turned. For simplicity it is advantageous toturn only switching elements in one selected section if the arrangementof connections shall be matched to a second section although it is inprinciple also possible to turn selected switching elements in both ofthese sections.

The connections of the turned switching elements to other switchingelements are retained if the other switching elements are disposed in astage in which at least one switching element is turned. In contrast, ifthe other switching elements are disposed in a stage in which noswitching element is turned the connections of the turned switchingelements to other switching elements are swapped in step 812. Often thiswill mean that the connections of the switching element are retained onone side, e.g. at the inputs, while the connections on the other side ofthe switching element, e.g. at the outputs, are swapped. Naturally, if aswitching element has only a single input or a single output thisconnection is retained. The swapping avoids unnecessary crossings ofconnections and restores an equal arrangement of the connectionscompared to the corresponding element in another section which is notturned.

The steps of turning and swapping are performed in such a way that thearrangement of the connections within at least one section correspondsto the arrangement of the connections within at least one furthersection with an equal number and arrangement of the switching elements.Preferably, all sections have equal arrangements and connections afterthese steps.

Traditionally, a Bene{hacek over (s)} network is built up in such a way,that connections between the outer stages connect switching elementsremotely located from each other, i.e. switching elements which may bein another section. In contrast, connections in the inner stages connectneighboring switching elements which are generally located in the samesection unless the number of sections is too high. In this case, theturning of the switching elements can be limited to the outer stages,i.e. to a limited number of stages adjacent to the ports. If each stageis subdivided between two sections only, only switching elements in thetwo outermost stages need to be turned to achieve an equal arrangementof the connections within the sections. If each stage is subdividedbetween four sections, only switching elements in the three outermoststages need to be turned to achieve an equal arrangement of theconnections within the sections because also connections between the 2ndand 3rd stage interconnect switching elements in different sections etc.

Turning switching elements as described above has the result, that thearrangement of connections between the sections will be different, e.g.the arrangement of the connections crossing the borders of sections isor becomes asymmetric. This is however not a significant disadvantagebecause connections crossing the borders need to be made via thebackplane supporting the sections or via other connections between thesections. The corresponding connections between switching elements indifferent sections are therefore adapted accordingly in step 814 so thatthe connections before the step of subdividing are retained.

Generally, connections between two switching elements in differentsections of the switching matrix can be subdivided into three segments.A first segment in a first section connects the first switching elementto a first contact in this section. A second segment in a second sectionconnects the second switching element to a second contact. In betweenboth contacts is a third segment of the connection for connecting thecontacts. Generally, the first segment will be on a circuit boardcarrying the first section of the switching matrix and the firstcontact. The second segment will be on the circuit board carrying thesecond section and the second contact. The third segment is generallypart of the backplane or another connection between the circuit boards.According to the above procedure, any first and second segments can bearranged in the same way in the respective sections. Only thearrangements of any third segments crossing the borders between thesections differ. In other words, all sections comprise equally arrangedcontacts and equally arranged segments of the connections between theswitching elements and the contacts.

It is advantageous if connections between different sections of theswitching matrix exist only between a limited number of stages while theconnections between other stages connect exclusively switching elementswithin the same section. In this way, the interconnection of thesections is simplified.

The above step of adapting the number of switching elements comprisespreferably to specify an equivalent regular Bone network. The equivalentregular Bene{hacek over (s)} network comprises a number of ingress portsequal to the number of egress ports and being the smallest power of 2which is at least equal to the number of ingress ports and at leastequal to the number of egress ports specified for the switching matrix.Thus the regular Bene{hacek over (s)} network can accommodate theswitching matrix, i.e. the network of the switching matrix, which isthen a subsection of the regular Bene{hacek over (s)} network. In thisway, the reduced Bene{hacek over (s)} network can be obtained in an easyway from the regular Bene{hacek over (s)} network by removal ofconnections and/or switching elements.

Optionally, the step of adapting can comprise to adapt the type of theswitching element by replacing at least one switching element with aswitching element with a smaller number of inputs and/or a smallernumber of outputs, e.g. a 2×2 switching element by a 2×1 or 1×2switching element. This option can considerably reduce the productioncosts, in particular if a 2×2 switching element comprises two relayswhile a 2×1 or 1×2 switching element comprises only a single relay.

Due to the retaining or swapping of connections, the step of movingswitching elements changes only their position within a stage. To obtainidentical arrangements of the switching elements within the sections itcan in particular be required to move a switching element within a stageinto a different section. Preferably, the step of moving is performedonly for switching elements in the stages adjacent to ports or in alimited number of stages adjacent to the ports. With an increasingnumber of sections, it may be required to move switching elements in anincreasing number of the next inner stages.

If turned switching elements are connected to ports of the matrix, theposition of the ports is exchanged. Accordingly, it is preferable if thedesignations of ports are adapted, e.g. swapped, in order to have asystematic arrangement of the port designations. In view of suchoptional adaptations, connections of a turned switching element to portscan either be retained or swapped.

Preferably, pairs of interconnected switching elements are turned inadjacent stages of a section. This allows an effective execution of theabove method as also the interconnection of both elements is rearrangedaccordingly in this step. Turning pairs of interconnected switchingelements is particularly effective if the other connections of theturned pair of switching elements between the stages, in which theelements are disposed, are connections over a border of sections,especially over a border perpendicular to the stages.

It should finally be noted that the step of subdividing in the abovemethod can be performed before the step of adapting the number ofswitching elements and connections. This is for example advantageous ifthe stages are subdivided into n sections and the number of ingress oregress ports deviates from 2n. Instead of splitting a 2×2 switchingelement it can be replaced in this case by two 1×2 switching elements,one in each section. While this increases the number of switchingelements compared to the number obtainable without a subdivided matrixthe method is still applicable. Similarly, it may be necessary toperform the step of moving before the step of subdividing.

Once a switching matrix is specified as described above, the sections ofthe switching matrix and the backplane can be produced according to thespecification and assembled to create the switching matrix. The sectionsspecified according to any of the different embodiments of the method asdescribed above can be cost-effectively produced.

The described method has the biggest advantages, if all sections of aswitching matrix are equal. Nonetheless, the advantages can often atleast partly be achieved if only some sections are equal or if sectionsare only substantially equal. In particular, it is possible thatselected switching elements are omitted in a section which was specifiedas described above, e.g. if ports are not needed. It is also possiblethat selected additional components are disposed in a section as long asthe switching matrix is specified as described above.

The method can also be embodied in a program comprising code forperforming the steps of the method.

An example of the above method is now described with respect to FIG. 6.As already mentioned, the left side of the figure shows a Bene{hacekover (s)} network with the central stage S4. In accordance with step 802the number of connections from ports to the uppermost stage S1 and ofconnections to ports from the lowermost stage S7 is specified to 12each. According to step 804, the number and type of switching elementsis adapted accordingly by removing selected elements or by replacing 2×2with 2×1 elements.

Subsequently it is specified that the matrix is subdivided into 4sections separated by bold lines on the right side of FIG. 6 whichrepresent the borders of the sections. Switching elements in the centralstage are in all 4 sections to avoid that they need to be functionallysplit. By moving elements within and between the stages it is ensuredthat the arrangement of the switching elements and of the externalconnections of all sections is equal.

However, this does not lead to equal arrangements of the connections inall sections. For this purpose switching elements are turned by 180°around the vertical axis, i.e. the axis perpendicular to the stages. Theorientation of a switching element is indicated by a vertical line,which is either on the left side or on the right side (see e.g. theelements in the 2nd stages 82, S2, S7). It should be noted that turning2×2 switching elements by 180° results in identically oriented switchingelement, in particular as the inputs can be connected either in parallelor crossed to the outputs. Also the turning of 2×1 switching elements by180° results in identically oriented switching elements. Nonetheless,the turning has an effect on the connections which are rearranged due tothe turning. As the arrangement of the connections and switchingelements in the inner stages S3-S5 is symmetrical from the start onlyelements in the outer stages S1, S2, S6 and S7 need to be turned.

In line with the principles outlined above, only the switching elementsin two of the sections, i.e. the upper right and the lower left section,are turned in the outer stages S1, S2, S6 and S7. The turning isperformed pair wise, i.e. two neighboring interconnected switchingelements in two adjacent stages are turned together, for exampleswitching element 2 in stage S1 and switching element 5 in stage S2.Finally, for each turned switching element in stage S2 both connectionsto the switching elements in stage S3 are swapped, i.e. interchanged. Inthe same way, the connections of the turned switching elements in stageS6 to switching elements in stage S5 are swapped. As the turning of theswitching elements by 180° interchanges the positions of both inputs oroutputs, the swapping of the connections ensures that the arrangement ofthe connections is unchanged by interchanging them, too.

The results of these steps is that both the arrangement of theconnections and the arrangement of the switching elements is identicalin all four sections except for those connections leading to anothersection, e.g. via the backplane. However, connections between thesections of the switching matrix are made separately in different stepsof the production such that asymmetries of these connections do notaffect the production costs of the sections and thus the switchingmatrix.

An advantageous switching matrix can be used for connecting selectedingress ports to selected egress ports over a Bene{hacek over (s)}network. The Bene{hacek over (s)} network comprises a plurality ofinterconnected switching elements. Each switching element has at leastone input and at least one output and is adapted to connect a selectedinput to a selected output of the switching element. The switchingelements are arranged in stages. The at least one input of any of theswitching elements has a connection to the at least one output of one ofthe switching elements in a preceding stage or to one of the ingressports. The at least one output of any of the switching elements has aconnection to the at least one input of one of the switching elements ofa subsequent stage or to one of the egress ports.

It is proposed that the switching matrix has a first number of ingressports and a second number egress ports. At least one of said numbersdeviates from an integer power of 2 or from the other number. The numberof switching elements and the number of connections between theswitching elements are adapted to the numbers of ports. The switchingmatrix is subdivided into a plurality sections such that at least two ofthe sections comprise an equal number of switching elements and an equalnumber of ports. The arrangement of the ports and the switching elementsin said sections is equal. Also the arrangement of the connectionswithin the sections is equal. Deviations in the arrangement ofconnections are limited to connections between the sections.

The switching matrix can be specified according to any embodiments ofthe method as described above. In particular, it is advantageous if thenumber of ingress ports is equal to the number of egress ports and ifall sections comprise an equal number and arrangement of ports andswitching elements.

The invention can also be embodied in a circuit board for a section ofthe switching matrix. The circuit board comprises the connections withinat least one of the sections. In this way positions for the switchingelements, in particular contacts for the inputs and outputs, are definedon the circuit boards as well as contacts for connections to othercircuit boards. Correspondingly, the above switching matrix can bemanufactured by disposing the switching elements at the correspondingpositions and attaching the connections to the contacts. It should benoted that the same circuit board can be used for different embodimentsof the switching matrixes, e.g. if not all positions are equipped withswitching elements but, depending on the number of required ports, someswitching elements are omitted. In this way, the above advantages in thedesign of the circuit board are maintained while a flexible andcost-effective production is possible.

The above embodiments admirably achieve the objects of the invention.However, it will be appreciated that departures can be made by thoseskilled in the art without departing from the scope of the inventionwhich is limited only by the claims.

The invention claimed is:
 1. A method to specify a switching matrix forconnecting selected ingress ports to selected egress ports over aBene{hacek over (s)} network, wherein the Bene{hacek over (s)} networkcomprises a plurality of interconnected switching elements, eachswitching element has at least one input and at least one output and isconfigured to connect a selected input to a selected output of theswitching element, wherein the switching elements are arranged in stagesand wherein the at least one input of any of the switching elements hasa connection to the at least one output of one of the switching elementsin a preceding stage or to one of the ingress ports, and wherein the atleast one output of any of the switching elements has a connection tothe at least one input of one of the switching elements in a subsequentstage or to one of the egress ports, characterized by the steps of:specifying a first number of ingress ports and a second number of egressports of the switching matrix, wherein at least one of said numbersdeviates from: an integer power of 2; wherein the first number ofingress ports differs from the second number of egress ports;configuring the number of the switching elements and the number of theconnections between the switching elements to the specified numbers ofports; subdividing the switching matrix into a plurality sections;moving the switching elements and the ports such that at least two ofthe sections comprise an: equal number and arrangement of the switchingelements and an equal number and arrangement of the ports, wherein theconnections are retained; in at least one of the at least two sections,turning switching elements having a connection to a switching element inanother of the plurality of sections such that the positions of theinputs are interchanged and/or the positions of the outputs areinterchanged; retaining the connections of the turned switching elementsto other switching elements if the other switching elements are disposedin a stage in which at least one switching element is turned andswapping the connections of the turned switching elements to otherswitching elements if the other switching elements are disposed in astage in which no switching element is turned; wherein the steps dturning and swapping are performed such that the arrangements of theconnections within the at least two sections correspond to each other.2. The method according to claim 1, wherein the step of configuringcomprises to specify an equivalent regular Bene{hacek over (s)} network,wherein the regular Bene{hacek over (s)} network comprises a number ofingress ports being the smallest power of 2 which is at least equal tothe first number of ingress ports and at least equal to the secondnumber of egress ports, and wherein the switching matrix is a subsectionof the regular Bene{hacek over (s)} network.
 3. The method according toclaim 1, wherein the switching elements comprise 2×2 units with 2 inputsand 2 outputs.
 4. The method according to claim 1, wherein the switchingelements comprise relays.
 5. The method according to claim 1, whereinsaid step of configuring comprises replacing at least one switchingelement with a switching element with a smaller number of inputs and/ora smaller number of outputs.
 6. The method according to claim 1, whereinsaid step of moving is performed only for switching elements in alimited number of stages adjacent to ingress or egress ports.
 7. Themethod according to claim 1, wherein the turning of switching elementsis restricted to stages with connections crossing a border of a section,wherein the border is perpendicular to the stages.
 8. The methodaccording to claim 1, wherein pairs of interconnected switching elementsare turned in adjacent stages of a section.
 9. A switching matrix forconnecting selected ingress ports to selected egress ports over aBone{network, wherein the Bene{hacek over (s)} network comprises aplurality of interconnected switching elements, each switching elementhaving at least one input and at least one output and being configuredto connect a selected input to a selected output of the switchingelement, wherein the switching elements are arranged in stages andwherein the at least one input of any of the switching elements has aconnection to the at least one output of one of the switching elementsin a preceding stage or to one of the ingress ports, and wherein the atleast one output of any of the switching elements has a connection tothe at least one input of one of the switching elements of a subsequentstage or to one of the egress ports wherein the switching matrix has afirst number of ingress ports and a second number egress ports, whereinat least one of said numbers deviates from an integer power of 2;wherein the first number of ingress ports differs from the second numberof egress ports; the number of switching elements and the number ofconnections between the switching elements are configured to the numbersof ports; the switching matrix is subdivided into a plurality sectionssuch that at least two of the sections comprise an equal number ofswitching elements and an equal number of ports, wherein the arrangementof the ports and the switching elements in said sections is equal; thearrangement of the connections within the sections is equal; anddeviations in the arrangement of connections are limited to connectionsbetween the sections.